This invention relates to interactive graphic display systems and in particular to cursor apparatus for providing graphic data entry in such systems.
Graphic display systems are used to process maps and other similar graphical information sources and generally include a console having a display screen and a flying spot type indicating and feature tracing means for tracing and performing interactive editing of displays. As such, there is commonly required a direct data coordination interaction between display surface and a digital feature file. Graphic data entry is a necessary feature of the interactive graphic display. This is required in order to enter new information into the digital data base as well as to designate already digitized features for the purpose of requesting additional information, modification, shifting, or removal.
The required information can be obtained by use of a sensor or movable cursor. State-of-the-art devices of this type are represented by the "quad cell" type sensor disclosed in the U.S. patents: Beam Detector Detector Hans Sorensen, U.S. Pat. No. 3,435,232; Optical Prism With Multiple Photo Cells, G. K. Nutz et al., U.S. Pat. No. 3,478,219; Light Sensing Device Having Polyhedra Reflectors and a Photomultiplier With Segmented Photocathode, H. L. Mondpar, U.S. Pat. No. 3,654,475; Direct Measurements of Ship Body Distortion Using a Laser Beam, G. W. Cook et al., U.S. Pat. No. 3,790,276; and Apparatus For Automatic Tracking of Pupil Of Eye, Ludwig Leity, U.S. Pat. No. 3,806,725.
In all the above concepts, the attitude of the sensor must be carefully controlled. Rotation of the sensor will reduce the servo loop gain, induce cross coupling between x and y channels, and even reverse the polarity of the feedback causing complete failure of the beam tracking servo. Such a restriction on sensor attitude is not desirable for a hand held cursor as it requires some sort of sliding mechanical arm to prevent the operator from rotating the cursor. The device described herein is a sensor with circular symmetry and may be picked up and held against the screen without operator's concern for proper rotation. Such an approach which uses a small circular dither rather than a full raster as one would use on a CRT with a light pen has various advantages. For instance, the circular dither makes more efficient use of the available pointing laser power and deflector bandwidth as the pointing beam only deviates from the sensor enough to indicate the direction and sign of pointing errors. In a raster scanning system, large deflection bandwidths are required tocover the entire screen at speeds above the flicker rate of the eye. In addition, a raster scan would waste most of the laser power by directing it to parts of the screen that are not of interest.